Both exterior and interior surfaces, substrates of all types and organic compositions and formulations, when exposed to common environmental conditions, e.g. moisture, are prone to attack, discoloration and various kinds of destruction by a variety of species of microorganisms, including fungi, algae, bacteria and protozoa. As a result, there has always been a great need for an effective and economical means to protect, for extended periods of time, both exterior and interior surfaces, various types of substrates and commercial compositions and formulations from the deterioration and destruction caused by such microorganisms.
Materials which need protection with a suitable antimicrobial composition for controlling microorganisms and their adverse effects include, for example, biodegradable compositions including such materials as paints and other coating formulations, surfactants, proteins, starch-based compositions, inks, emulsions and resins, stucco, concrete, stone, and cementaceous surfaces, wood, caulking, sealants, leather, plastics, and textiles as well as materials and other substances which may be attacked by destructive microbes, especially fungi and/or algae. Polymer dispersions or aqueous latex paints containing polyvinyl alcohol, polyacrylates or vinylpolymers, thickener solutions containing cellulose derivatives, kaolin suspensions and metal working fluids, also are prone to degradation by the action of objectionable microorganisms, which can significantly impair the usefulness of such compositions. Such degradation produces changes in pH values, causes gas formation and discoloration and the formation of objectionable odors, and may produce changes in rheological properties.
Wooden objects, in particular, are subject to degradation from a wide variety of natural pests. Fungi are particularly prevalent and include brown rots, white rots and soft rots. Fortunately, a variety of compositions have been developed for treating wooden objects and other materials and surfaces to retard the destructive effect of such pests.
An enormously wide variety of materials have been identified which, to various degrees, are effective in retarding or preventing the growth of, and accompanying destruction caused by, such microbes in such circumstances. Such biocidal compounds include halogenated compounds, organometallic compounds, quaternary ammonium compounds, phenolics, metallic salts, heterocyclic amines, formaldehyde donors, organosulfur compounds and the like.
One well-known class of biocides used in such coating compositions are those containing a halopropynyl moiety, and especially an iodopropynyl moiety. Such compounds are widely disclosed in the patent literature including U.S. Pat. Nos. 3,660,499; 3,923,870; 4,259,350; 4,592,773; 4,616,004 and U.S. Pat. No. 4,639,460 to name a few. Included within this class of compounds are the halopropynyl carbamates which are known primarily for their fungicidal activity. 3-iodo-2-propynyl butyl carbamate, hereinafter also referred to as IPBC, is one of the best known and probably the most widely used of the halopropynyl carbamate fungicides. IPBC is a highly active broad spectrum fungicide. In addition to its fungicidal activity, IPBC also has been associated with algaecidal activity. In this regard, Great Britain Patent 2,138,292 and U.S. Pat. No. 4,915,909 and U.S. Pat. No. 5,082,722 contain such disclosures.
One of the most common ways to apply such materials to surfaces, including wooden objects, to prevent microbial attack is to include them in a composition used to coat the object. The coating, in the form of paints, lacquers and varnishes, functions as a vehicle for the biocidal agent and acts as a barrier to the natural elements, such as sunlight and precipitation. One widely used coating formulation contains an alkyd resin, an oil, an optional solvent thinner and a drier. Another is based on a latex resin emulsion in an aqueous vehicle. Such compositions form dried film coatings by a combination of solvent evaporation, resin oxidation and polymerization.
Haloalkynyl compounds, including halopropynyl compounds, and especially the halopropynyl carbamates, are formulated with a variety of other ingredients in both aqueous and organic solvent mixtures to form such coating materials. For various reasons, it is desired that these coating compositions maintain their biocidal activity for prolonged periods of time.
Unfortunately, this class of biocides is prone to degradation by a variety of mechanisms. One recognized degradation pathway involves ultraviolet (UV) radiation and is primarily a problem in dried coatings containing such biocides. Halopropynyl compounds, and particularly IPBC, are subject to photo-oxidation reactions when exposed to light and are likely to decompose when exposed to sunlight. Organic iodine compounds, in particular, form elemental iodine and other free radical fragments that appear yellow to brown in color. As a result, exposure of surfaces, including dried paint films, containing such compounds, to light causes discoloration and yellowing. This discoloration is especially objectionable in compositions where a white color is desired such as in white caulks, white paints, paper coatings, plastic coatings and the like. Not surprisingly, the prior art has proposed ways of combating the light induced degradation of these halopropynyl compounds.
Gabriele et al., in U.S. Pat. No. 4,552,885 and in Gabriel et al., Journal of Coatings Technology, 56(712):33-48, disclose using a 2,2,6,6-tetraalkylpiperidine compound and/or a UV absorber as a way of stabilizing organic fungicidal formulations against light-induced (and particularly ultra-violet light induced) degradation. Such formulations include paints, substrate treatments and protective coatings. IPBC is included in the list of fungicides identified in the patent and is illustrated in the examples.
Singer U.S. Pat. No. 4,276,211 describes adding an organic epoxide stabilizer to compositions containing iodoalkyne carbamates, such as IPBC, to reduce discoloration. Long, U.S. Pat. No. 4,297,258 also recommends using epoxides to reduce the tendency of such fungicides to yellow.
Notwithstanding these prior attempts to reduce the tendency of compositions containing a halopropynyl compound, and particularly a halopropynyl carbamate fungicide such as IPBC, to discolor upon exposure to light, particularly sunlight, and/or heat, the art continues to look for alternative solutions to the discoloration problem.
The present invention provides an improved way to stabilize halopropynyl compounds, and particularly a halopropynyl carbamate fungicide such as IPBC (known in commerce as Troysan Polyphase.RTM.), not only in a dry film coating, but also in a wet formulation such as a latex paint, against light and/or heat induced degradation and discoloration.